What happens to your heart rate when you exercise and why

Cardiovascular exercise involves the use of large muscles in a repetitive fashion, activating muscle fibers programmed for endurance and utilizing a heart rate range anywhere from 40 to 85 percent of your maximum heart rate. Think: running, jogging, swimming, biking, or spinning.

How does cardiovascular exercise affect your heart?

When performing cardio, blood flow is directed toward working muscles and away from areas that aren't doing much (such as your arms during running, or the digestive tract). There is increased blood flow, and blood volume returning to the heart.

As the heart registers a larger blood volume, over time the left ventricle adapts and enlarges. This larger cavity can hold more blood, and ejects more blood per beat, even at rest.

More: Calculate your Target Heart Rate.

Over time, with chronic cardio training, our resting heart rate drops because each beat delivers a bigger burst of blood, and fewer beats are needed. This takes work off your heart and is why cardio exercise is recommended for heart health.

However, cardiovascular exercise can also produce stress. If we get into over-training, we may hit a point where we are drowning in cortisol. This eventually leads to immune-suppression and fat gain around the abdomen and face.

People who spend a significant part of their day in stress, who have poor digestion or other sources of physiological stress, should not further their stress levels by overtraining. Always think of your goals, moderate your exercise if necessary, and work to reduce your stress levels.

How does strength training exercise affect your heart?

Strength training exercise works the heart in a completely different way. At any given moment, certain muscles are contracting and relying predominantly on type two muscle fibers, which are responsible for giving us a great looking body and making us stronger.

As the muscles contract—say the arm muscles during a bicep curl—they press and close the blood vessels that flow through them. This leads to increased blood pressure in the rest of the body and the heart has to fight against a stronger force to push blood out.

The heart adapts to this by increasing the thickness of the left ventricle wall. This thickness derived from chronic weight training is healthy, whereas the thickness from chronic high blood pressure is not.

What's the difference? The healthy heart only has to work under pressure for two to three hours of strength training per week, whereas the heart with high blood pressure has to work 24 hours a day, seven days a week. The second heart may exhaust, whereas the healthy heart becomes stronger with a lower resting heart rate.

Exercise also stimulates the production of new blood vessels. As we make more blood vessels, there are more places for blood to flow, which results in more efficient circulation. Cardiovascular exercise increases the number of new blood vessels while resistance training increases the size of those blood vessels.

Stick to a smart, well-designed exercise program and pay special attention to your diet. Practice healthy eating and stress-reduction techniques. Exercise can naturally lower blood pressure to normal limits when combined with stress reduction and an effective dietary approach.

This activity is a great way to introduce correct scientific procedures, thinking about variables to change and keep constant.

Exercise increases the rate at which energy is needed from food, increasing the need for both food and oxygen by the body. This is why when we exercise both pulse/heart rate and breathing rate increase.

Pulse rate is  an indication of your heart rate as your arteries expand each time the ventricles pump blood out of the heart.

The heart speeds up to pump extra food and oxygen to the muscles, while breathing speeds up to get more oxygen into the body and remove carbon dioxide.

How does exercise affect heart rate investigation

Step 1

Use the stethoscopes and timers to record how many heartbeats you can hear in 30 seconds.

Step 2

Exercise – this could be 30 seconds of star jumps or a mini obstacle course. 

Step 3 

Use the timers and stethoscopes again to record how many heartbeats you can hear in 30 seconds.

Let’s think scientifically

A scientific investigation should be a fair test, think about what conditions you need to keep the same and what condition you will change. You should also repeat the testing 3 times and find the average heart rate.

Things to keep the same:

Heartbeats must be counted before and after exercising for the same amount of time.

The person whose heart rate is compared must be the same.

Things to change: 

Heart rate should be measured before and after exercise.

Make a prediction

What effect do you think exercise will have on heart rate?

Why do you think this?

Clue – when you exercise your muscles need more food and oxygen from your blood, so your heart has to beat faster to transport them.

What is recovery time? 

Recovery time is the time taken for heart rate to return to normal. If you have time, can you work out how long this is for you?

The pulse rate and breathing rate of a fitter person rise much less than in an unfir person during exercise, fitter people also have a shorter recovery time.

Links to Maths

Design a method of recording your results? Can you work out the average heart rate for 10 participants before and after exercise?

Calculate the difference between a person’s heart rate before and after exercise.

Links to English

Can you write a letter to a friend telling them about your findings?

More Science for Kids

Find out how to make your own stethoscope with a funnel, tape and cardboard tube.

Make a pumping model of a heart, or try one of our sports science investigations.

Suitable for:

Key Stage 1 Science: Animals including Humans

Describe the importance for humans of exercise, eating the right amounts of different types of food, and hygiene.

Key Stage 2 Science: Animals including Humans

Recognise the impact of diet, exercise, drugs and lifestyle on the way their bodies function

Last Updated on June 17, 2021 by